Passive Optical Network System and Optical Line Terminal

1. An optical line terminal comprising: an OE converter; an identification unit for identifying the output of the OE converter with respect to the value 0 or 1 using a threshold; and a controller for controlling the identification unit, wherein said controller provides the identification unit with a first offset in the period of receiving a ranging transmission and provides the identification unit with a second offset which is smaller than the first offset, a period other than the period of receiving the ranging transmission, wherein said identification unit calculates the threshold for identification, based on the first offset or the second offset which is provided by the controller.

2. The optical line terminal according to claim 1 , further comprising a selector for selecting one of the first offset and the second offset and for outputting the one, wherein said controller provides the identification unit with one of the first offset and the second offset by control of the selector.

3. An optical line terminal having an OE converter and first and second identification units which identify the output of the OE converter with respect to the value 0 or 1 using a threshold, comprising: a selector for selecting one of the first and second identification units; and a controller which control the selector so that the selector selects the first identification unit in the period of receiving a ranging transmission and selects the second identification unit in the period of other than the period of receiving a ranging transmission, wherein said first identification unit uses a first threshold which is calculated based on a first offset, wherein said second identification unit uses a second threshold which is calculated based on a second offset, and wherein said second offset is smaller than the first offset.